1. Field of the Invention
The present invention relates to a projection apparatus and a projection control method, which fit for use as, for example, a data projector capable of projecting stereoscopic images.
2. Description of the Related Art
Hitherto, projectors of the Digital Light Processing (DLP) (trademark) type have been commercialized. In recent years, various techniques have been devised, which enable the projectors of the DLP type to project stereoscopic images (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2007-536576.)
To project a stereoscopic image with a projection using liquid-crystal shutter eyeglasses of ordinary type, sync pulses of much higher luminance than the projected image must be inserted in the left-eye and right-eye video signals, respectively, when projecting the image, so that the light-receiving elements at the liquid-crystal shutter eyeglasses may the sync signals, respectively, because of the difference in luminance level, when the left-eye image is switched to the right-eye image, or vice versa.
In any DLP projector that has color wheel having a plurality of color filters arranged along the circumference and a white light source such as high-pressure mercury lamp, the sync pulses are transmitted at the time the light beams pass the transparent white (W) filter.
In recent years, projectors have been put on the market, each projector using light-emitting diodes (LEDs) or laser diodes (LD, or semiconductor lasers) in place of the white light source.
In the projector of this type, each semiconductor light-emitting element basically emits a beam of one color only. Hence, a plurality of semiconductor light-emitting elements are driven in time-division, performing field-sequential light emission to display a color image.
Therefore, in any projector using various types of semiconductor light-emitting elements, at least two types are driven at the same time to generate a sync pulse obviously different in luminance from the sync pulse for any other field for which the elements of one type are driven.
In a projector having two semiconductor light-emitting elements, one being an LD capable of generating blue or green light by using a color wheel, and the other being a red-emitting LED, the LD emits green light of higher luminance than blue light it can emit. Hence, the LD and the LED are simultaneously driven, emitting a green light beam and a red light beam at the same time, generating a sync pulse for yellow, i.e., mixture of green and red, thereby to control the timing of switching the stereoscopic images.
In this case, the yellow light for the sync pulse influences the viewer's visual perception, making the viewer perceive any black part as yellowish, in an image that is dark because of dark pictures projected continuously, though how much yellowish the black part appears differs from viewer to viewer. Consequently, the dark image looks very unnatural in some cases.